Heavier crudes are, by definition, more viscous. The also contain greater amounts of sulfur, which must be removed because of the adverse impact of sulfur on various catalysts used in the refining process. The sulfur content of fuel is also controlled because of its impact on particulate generation....

Prior posts have noted the adverse health impacts from small particles, often referred to generally as PM10 and/or PM2.5. Prior posts have also noted the adverse impact of soot on global warming, which because it is black and absorbs heat warms up the atmosphere and whatever it is coating (e.g., glaciers...